1. Field of the Invention
The disclosure herein relates generally to a tri-cone bit. More particularly, the disclosure relates to a tri-cone bit for high RPM drilling applications in subterranean exploration and petroleum drilling industries.
2. Description of Related Art
Current tri-cone bit typically comprises a bit body. The bit body has three head sections, with a cantilevered bearing shaft at a lower end of each head section, and three cones each of which is mounted on a corresponding bearing shaft. A bearing couple is formed by the bearing shaft and inner bore of the cone. The bearing couple transfers WOB and torque to the cone. At present, journal bearing and roller bearing are two major bearing types for roller cone bits. Cones can be machined with steel teeth or mounted with carbide inserts as cutting elements. Drilling fluid enters water course of the bit from drilling string and is then jetted out from three nozzles which are mounted in nozzle sockets on the bit. After impinging on the bottom of the well, the drilling fluid flows back upwardly from sides of the nozzle socket. The jet from the nozzles is directed to impinge on the space at midway between two adjacent cones in the vicinity of borehole wall. Three points on heel row inserts of the cone contact the borehole wall at a leading side of the cone.
Following problems occur when the existing bit is used on turbo drills or high speed down hole motors for high RPM drilling applications. (1) The bearing life is greatly decreased because a journal bearing cannot withstand high RPM and a roller bearing cannot withstand high WOB. (2) High RPM drilling is generally accompanied by high WOB. This would considerably increase the impact force acting on cutting elements of the bit, and thus the lateral and longitudinal vibrations of the bit become more serious. As a result, cutting elements of the bit wear fast and can be easily broken, consequently reducing the drilling efficiency. Besides, when high RPM bit is used to drill hard formation, heat can be generated on cutting elements fast by wear and if timely cooling cannot be achieved, premature failure of the cutting elements would occur.